Humming Keystone

 is an item in Tyranny.

Description
A scuffed but legible glyph has been scratched into this old, weathered shard. Stones like this are not uncommon in the Oldwalls, and often fit as keystones into larger structures. This particular stone vibrates gently when struck, producing an unpleasant hum.

Use

 * A Breach Between Worlds: Found at Blade Grave Oldwalls - Central in the central room. Fits into the lower left receptacle.